The operation of various designs of fluidized beds is well understood. As a general matter, fluidized beds are designed so as to suspend solid or liquid fuels on upward blowing jets of air during the combustion process. The result is a turbulent mixing of gas and the waste material. This tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer. In the past, fluidized bed combustion plants have been used for combusting various types of fuel into energy, and are considered to be more flexible than conventional energy plants in that they can be fired on coal, biomass and other fuels.
In burning solid or liquid fuels in a fluidized bed arrangement, all the combustible components of the fuel are generally converted to heat energy and gaseous byproducts, which mostly consist in the form of carbon dioxide and water. In previous fluidized bed arrangements that have been useful for combusting used-automotive tires, for example, most of the noncombustibles that are left following the combustion and/or gasification process comprise such byproducts as ash which may become entrained within the exhaust gas and removed from the process by the conveyance velocity of the exhausting gases. However, a small portion of the non-combustibles which remain within the fluidized bed are typically in the form of inert material of various sorts. This inert or noncombustible material is typically referred to as “tramp” in the industry. In the case of used, automotive tire derived fuel, this “tramp” may be comprised, at least in part, of the tire bead and/or belting wire used in the construction of the tire which can have a length of 1 to 7 inches depending upon the size of the tire chip that is used as a fuel in the fluidized bed. Of course, these resulting metal wires or beads are not combustible, but in some instances may oxidize, at least in part, to a level which allows some of these inert materials to become airborne, and then be removed by the resulting exhaust gases. The balance of any metal wires, and the like, remain within the fluidized bed environment. Individually, these wires are not detrimental to the combustion or fluidization process, but they tend to accumulate over time, and they further have a tendency to intertwine with one another and create various obstructive random structures or conglomerations. These twisted conglomerations of wires which have often been referred in the industry as “bird nests” may continue to grow in size until they disrupt fluidization and impede the sustained combustion and/or gasification of the automotive tire fuel within the fluidized bed. To prevent this disruptive event from occurring, these intertwined “bird nests” need to be eliminated from the fluidized bed. Inasmuch as automotive tires may contain as much as 10 percent wire or belt content, the accumulation of this type of non-combustible material can occur in a very short period of time and may readily and noticeably impair the operation of the entire fluidized bed.
Heretofore, to address the problem noted, above, operators of such prior art fluidized bed designs had no convenient means available to remove these “bird nests” made of non-combusted wire without first removing a significant portion of the sand from the fluidized bed. As should be understood, prior art fluidized beds have tended to operate in temperature ranges of about 1,200-1,900 degrees F. Consequently, any removal of significant volumes of sand and wire directly from these prior art fluidized bed designs created the potential for significant energy and temperature losses to be experienced in the overall process. Further, handling the sand and other inert material which had entrained “birds nests” within it, of course, creates operational and safety hazards which are readily obvious. Notwithstanding the presence of these several perceived problems, the art has failed to disclose any convenient means so that “birds nests,” which have become entrained within the sand of the fluidized bed, can be conveniently removed while not resulting in significant energy losses from the operational fluidized bed environment.
Therefore, a fluidized bed which achieves the benefits to be derived from the aforementioned technology, but which avoids the detriments individually associated with the operation of fluidized bed designs used heretofore is the subject matter of the present invention.